You might consider different options. Trijicon is the gold standard (I have the older dual illumination on a G17 with backup suppressor sights). It's the MOS version so has the slide already cut. As mentioned previously the best method is a milled slide with backup suppressor sights. The dual illumination can suffer target washout (bright target, dim surroundings); most of the 3rd generation RMRs have an auto-bright which solves this. Trijicon has not been without problems in their original series but the newer ones have largely solved this. Whatever you get, make sure you can change the battery without removing the sight.
It might be heresy but the Holosun 507c series is an excellent choice to consider as well (I had my reservations also). I've mounted one on the VP-40 with a dovetail mount (I'd not suggest this unless you have to because it precludes the backup irons). Many of my friends also have this series--it has an auto-off function as well as auto-bright and very long battery life. Mine and others have had excellent reliability with it. The NICE thing is that the reticle is very easy to acquire and you have different switching reticle choices in one of the versions (which are the easiest dots to acquire of any RMR I've used). One in particular is the large circle with center dot. The hardest thing to overcome is 'finding the dot' especially when shooting from non-conventional positions or around barricades. I'm not HUGELY concerned about the B/U sights in that the gun itself can be used as a course sight in very close encounters (most people IN these situations don't remember using the sights anyway).
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The nice thing about a dot is that everything stays on the same focal plane so you can stick with target centered focus and it helps aging eyes. But it does take LOTS of training to employ well.
ONE OTHER OPTION that you might consider is the XS sight series--specifically the DXT big dots (which have a dot the I luminous representation). I like the white or green option. These are NOT target sights though (although they can be shot accurately with practice); they're more of a running and gunning type of thing used in clearing a building or a dynamic situation under bad environmentals. You can get these cheaper and I have a set on my Sig C3 carry gun.
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Here's one type of setup of a dual illumination RMR with Trijicon backup sights (on a Glock)
And the Holosun with dovetail mount on a VP-40 (again if you could go the milled slide route it's better but the striker block on a VP-40 presents a few challenges when doing this--it can still be done but the axle needs modified so I went the dovetail mount route).